The man, who was not identified, did not mean any harm, saying he had forgotten that the ammunition was in his carryon bags when he boarded the flight, Transportation Security Administration spokesman Jim Fotenos said.

TSA agents turned the ammunition over to local police and sent the man back for another security search. They then allowed him to reboard and the plane left for Dallas later Monday.

"The passenger was interviewed and rescreened with negative findings," Fotenos said in a statement. "The passenger stated that he inadvertently brought the prohibited items onboard the plane and self-disclosed them when he realized they were in his possession."

Fotenos said the TSA is reviewing how the passenger got the ammunition through pre-boarding security searches. He declined to identify the man or comment further. TSA policy prohibits passengers from having firearms or ammunition in their carryon luggage.

Oak Creek, Wis. based-Midwest Airlines declined to comment.

The incident comes less than a week after a grand jury indicted Umar Farouk Abdulmutallab with trying to use chemical explosives stashed in his underwear to blow up a Northwest Airlines plane as it landed in Detroit on Christmas Day. Since then, the TSA and airlines have boosted security in airports in the U.S. and around the world.

Another passenger on Monday's Midwest Airlines flight 1669, Doug Bell, 50, of Hales Corners, Wis., said the plane was pushing back from the gate around 8 a.m. when the pilot came on the intercom and said there was a security problem and the plane had to return to the gate. The pilot said a passenger had notified a flight attendant he was a gun dealer and had shells in his bag, Bell said.

"There was a murmur on the plane," Bell said. "The whole plane was wondering what was going on. It isn't everyday the pilot tells you somebody got on the plane and brought shells with him. ... I couldn't believe it."

The man got off the plane and a TSA agent searched the luggage compartment above his seat, Bell said. The man then got back on board, and the plane took off after about an hour's delay, he said.

Bells said he was shocked TSA agents didn't search the entire plane because the man could have dropped off something in another seat as he walked back to his during boarding.

"Thankfully the man was an honorable man," Bell told The Associated Press in a telephone interview after the plane landed. (But) what if he wasn't so honorable? I'm telling you, security isn't working."